MULTIWAVELENGTH PROPERTIES OF ACTIVE GALACTIC NUCLEI

The emission of active galactic nuclei spans the electromagnetic spect rum from the far-infrared domain (or radio domain) to the gamma rays. This emission is made of a number of components, each described by a n umber of parameters which, at present, cannot be deduced from a compre hensive and self-consistent underlying model. The observations allow, however, to identify the physical origin of most of the components. Co rrelations between the light curves observed in different spectral dom ains have been found for few objects which have been intensively obser ved in the last few years. The observed lags have provided unexpected and important constraints for the interpretation of the emission compo nents.